Lead and zinc production involved crushing and grinding the mined rock to standard sizes and separating the ore. The remaining material or by product of this ore separation is known as “chat” or “tailings.” While some of the chat or tailings was deposited into the mine shafts once the mines were exhausted or abandoned, most of the chat and tailings were left behind in piles of leftover rock. For example, these “chat” and “tailings” piles cover over 40,000 acres in Cherokee County, Kansas, Ottawa and Craig Counties in Oklahoma, and Jasper County, Missouri, making it some of the most environmentally blighted land in the United States.
These wastes were also a source of contamination. Lead, zinc, and cadmium from the chat and tailings leached into the shallow ground water, contaminating local wells, and runoff moved contaminants into nearby streams and rivers. Wind also blew fine metal-bearing dust (from chat and tailings piles and roads made of chat and tailings) into the air, spreading the contamination to nearby non-mined areas.
It was attempted to dispose of the chat and tailings by depositing it back into the mines. However, the biggest problem faced was that the caverns in the mines were filled with water, that was contaminated. Simply dumping the chat and tailings 10 back down the mine casings (shafts) 12 into the caverns 14, formed between the mine roof 14a and the mine floor 14b, that either were or over time filled with water, did not spread the chat and tailings 10 in a volume efficient manner. Rather, the chat and tailings accumulated in a conical pile 15, as shown in FIG. 1.
As a result most of the space in the caverns 14, between the mine roof 14a and the mine floor 14b, was not filled (as shown in FIG. 1). Also, raw chat plugged the casings quickly. The chat was typically not screened for large particles, hindering the dumping process. Moreover, the chat and tailings just dumped into the casing 12 in this manner, as shown in FIG. 1, and eventually returned above the ground surface 16 in the form of toxic dust.
Additionally, the chat and tailings can not be put in large holes and ditches on the ground surface and buried therein, as the rock table is too close to the ground surface. Accordingly, there is simply not enough over burden to facilitate such a process.
With additional reference to the mine cavern 14, the total depth of the mine, from the surface 16 to the mine floor 14b is represented by the arrows labeled DT. The depth through the dirt/rock strata 18, from the surface 16 to the mine roof 14a is represented by the arrows labeled DM, and the mine cavern height, from roof 14a to floor 14b is represented by the arrows labeled HM.